### Function

# GLib spawn_async_with_pipes_and_fds

since: 2.68

#### Declaration [src]

    gboolean
    g_spawn_async_with_pipes_and_fds (
      const gchar* working_directory,
      const gchar* const* argv,
      const gchar* const* envp,
      GSpawnFlags flags,
      GSpawnChildSetupFunc child_setup,
      gpointer user_data,
      gint stdin_fd,
      gint stdout_fd,
      gint stderr_fd,
      const gint* source_fds,
      const gint* target_fds,
      gsize n_fds,
      GPid* child_pid_out,
      gint* stdin_pipe_out,
      gint* stdout_pipe_out,
      gint* stderr_pipe_out,
      GError** error
    )

#### Description [src]

Executes a child program asynchronously (your program will not block waiting for the child to exit).

The child program is specified by the only argument that must be provided, `argv`. `argv` should be a `NULL`-terminated array of strings, to be passed as the argument vector for the child. The first string in `argv` is of course the name of the program to execute. By default, the name of the program must be a full path. If `flags` contains the `G_SPAWN_SEARCH_PATH` flag, the `PATH` environment variable is used to search for the executable. If `flags` contains the `G_SPAWN_SEARCH_PATH_FROM_ENVP` flag, the `PATH` variable from `envp` is used to search for the executable. If both the `G_SPAWN_SEARCH_PATH` and `G_SPAWN_SEARCH_PATH_FROM_ENVP` flags are set, the `PATH` variable from `envp` takes precedence over the environment variable.

If the program name is not a full path and `G_SPAWN_SEARCH_PATH` flag is not used, then the program will be run from the current directory (or `working_directory`, if specified); this might be unexpected or even dangerous in some cases when the current directory is world-writable.

On Windows, note that all the string or string vector arguments to this function and the other `g_spawn*()` functions are in UTF-8, the GLib file name encoding. Unicode characters that are not part of the system codepage passed in these arguments will be correctly available in the spawned program only if it uses wide character API to retrieve its command line. For C programs built with Microsoft’s tools it is enough to make the program have a `wmain()` instead of `main()`. `wmain()` has a wide character argument vector as parameter.

At least currently, mingw doesn’t support `wmain()`, so if you use mingw to develop the spawned program, it should call `g_win32_get_command_line()` to get arguments in UTF-8.

On Windows the low-level child process creation API `CreateProcess()` doesn’t use argument vectors, but a command line. The C runtime library’s `spawn*()` family of functions (which `g_spawn_async_with_pipes()` eventually calls) paste the argument vector elements together into a command line, and the C runtime startup code does a corresponding reconstruction of an argument vector from the command line, to be passed to `main()`. Complications arise when you have argument vector elements that contain spaces or double quotes. The `spawn*()` functions don’t do any quoting or escaping, but on the other hand the startup code does do unquoting and unescaping in order to enable receiving arguments with embedded spaces or double quotes. To work around this asymmetry, `g_spawn_async_with_pipes()` will do quoting and escaping on argument vector elements that need it before calling the C runtime `spawn()` function.

The returned `child_pid` on Windows is a handle to the child process, not its identifier. Process handles and process identifiers are different concepts on Windows.

`envp` is a `NULL`-terminated array of strings, where each string has the form `KEY=VALUE`. This will become the child’s environment. If `envp` is `NULL`, the child inherits its parent’s environment.

`flags` should be the bitwise OR of any flags you want to affect the function’s behaviour. The `G_SPAWN_DO_NOT_REAP_CHILD` means that the child will not automatically be reaped; you must use a child watch (g_child_watch_add()) to be notified about the death of the child process, otherwise it will stay around as a zombie process until this process exits. Eventually you must call `g_spawn_close_pid()` on the `child_pid`, in order to free resources which may be associated with the child process. (On Unix, using a child watch is equivalent to calling `waitpid()` or handling the `SIGCHLD` signal manually. On Windows, calling `g_spawn_close_pid()` is equivalent to calling `CloseHandle()` on the process handle returned in `child_pid`). See g_child_watch_add().

Open UNIX file descriptors marked as `FD_CLOEXEC` will be automatically closed in the child process. `G_SPAWN_LEAVE_DESCRIPTORS_OPEN` means that other open file descriptors will be inherited by the child; otherwise all descriptors except stdin/stdout/stderr will be closed before calling `exec()` in the child. `G_SPAWN_SEARCH_PATH` means that `argv`[0] need not be an absolute path, it will be looked for in the `PATH` environment variable. `G_SPAWN_SEARCH_PATH_FROM_ENVP` means need not be an absolute path, it will be looked for in the `PATH` variable from `envp`. If both `G_SPAWN_SEARCH_PATH` and `G_SPAWN_SEARCH_PATH_FROM_ENVP` are used, the value from `envp` takes precedence over the environment.

`G_SPAWN_CHILD_INHERITS_STDIN` means that the child will inherit the parent’s standard input (by default, the child’s standard input is attached to `/dev/null`). `G_SPAWN_STDIN_FROM_DEV_NULL` explicitly imposes the default behavior. Both flags cannot be enabled at the same time and, in both cases, the `stdin_pipe_out` argument is ignored.

`G_SPAWN_STDOUT_TO_DEV_NULL` means that the child’s standard output will be discarded (by default, it goes to the same location as the parent’s standard output). `G_SPAWN_CHILD_INHERITS_STDOUT` explicitly imposes the default behavior. Both flags cannot be enabled at the same time and, in both cases, the `stdout_pipe_out` argument is ignored.

`G_SPAWN_STDERR_TO_DEV_NULL` means that the child’s standard error will be discarded (by default, it goes to the same location as the parent’s standard error). `G_SPAWN_CHILD_INHERITS_STDERR` explicitly imposes the default behavior. Both flags cannot be enabled at the same time and, in both cases, the `stderr_pipe_out` argument is ignored.

It is valid to pass the same FD in multiple parameters (e.g. you can pass a single FD for both `stdout_fd` and `stderr_fd`, and include it in `source_fds` too).

`source_fds` and `target_fds` allow zero or more FDs from this process to be remapped to different FDs in the spawned process. If `n_fds` is greater than zero, `source_fds` and `target_fds` must both be non-`NULL` and the same length. Each FD in `source_fds` is remapped to the FD number at the same index in `target_fds`. The source and target FD may be equal to simply propagate an FD to the spawned process. FD remappings are processed after standard FDs, so any target FDs which equal `stdin_fd`, `stdout_fd` or `stderr_fd` will overwrite them in the spawned process.

`source_fds` is supported on Windows since 2.72.

`G_SPAWN_FILE_AND_ARGV_ZERO` means that the first element of `argv` is the file to execute, while the remaining elements are the actual argument vector to pass to the file. Normally `g_spawn_async_with_pipes()` uses `argv`[0] as the file to execute, and passes all of `argv` to the child.

`child_setup` and `user_data` are a function and user data. On POSIX platforms, the function is called in the child after GLib has performed all the setup it plans to perform (including creating pipes, closing file descriptors, etc.) but before calling `exec()`. That is, `child_setup` is called just before calling `exec()` in the child. Obviously actions taken in this function will only affect the child, not the parent.

On Windows, there is no separate `fork()` and `exec()` functionality. Child processes are created and run with a single API call, `CreateProcess()`. There is no sensible thing `child_setup` could be used for on Windows so it is ignored and not called.

If non-`NULL`, `child_pid` will on Unix be filled with the child’s process ID. You can use the process ID to send signals to the child, or to use `g_child_watch_add()` (or `waitpid()`) if you specified the `G_SPAWN_DO_NOT_REAP_CHILD` flag. On Windows, `child_pid` will be filled with a handle to the child process only if you specified the `G_SPAWN_DO_NOT_REAP_CHILD` flag. You can then access the child process using the Win32 API, for example wait for its termination with the `WaitFor*()` functions, or examine its exit code with `GetExitCodeProcess()`. You should close the handle with `CloseHandle()` or `g_spawn_close_pid()` when you no longer need it.

If non-`NULL`, the `stdin_pipe_out`, `stdout_pipe_out`, `stderr_pipe_out` locations will be filled with file descriptors for writing to the child’s standard input or reading from its standard output or standard error. The caller of `g_spawn_async_with_pipes()` must close these file descriptors when they are no longer in use. If these parameters are `NULL`, the corresponding pipe won’t be created.

If `stdin_pipe_out` is `NULL`, the child’s standard input is attached to `/dev/null` unless `G_SPAWN_CHILD_INHERITS_STDIN` is set.

If `stderr_pipe_out` is NULL, the child’s standard error goes to the same location as the parent’s standard error unless `G_SPAWN_STDERR_TO_DEV_NULL` is set.

If `stdout_pipe_out` is NULL, the child’s standard output goes to the same location as the parent’s standard output unless `G_SPAWN_STDOUT_TO_DEV_NULL` is set.

`error` can be `NULL` to ignore errors, or non-`NULL` to report errors. If an error is set, the function returns `FALSE`. Errors are reported even if they occur in the child (for example if the executable in ``argv`[0]`is not found). Typically the`message`field of returned errors should be displayed to users. Possible errors are those from the`G_SPAWN_ERROR` domain.

If an error occurs, `child_pid`, `stdin_pipe_out`, `stdout_pipe_out`, and `stderr_pipe_out` will not be filled with valid values.

If `child_pid` is not `NULL` and an error does not occur then the returned process reference must be closed using g_spawn_close_pid().

On modern UNIX platforms, GLib can use an efficient process launching codepath driven internally by `posix_spawn()`. This has the advantage of avoiding the fork-time performance costs of cloning the parent process address space, and avoiding associated memory overcommit checks that are not relevant in the context of immediately executing a distinct process. This optimized codepath will be used provided that the following conditions are met:

1. `G_SPAWN_DO_NOT_REAP_CHILD` is set
2. `G_SPAWN_LEAVE_DESCRIPTORS_OPEN` is set
3. `G_SPAWN_SEARCH_PATH_FROM_ENVP` is not set
4. `working_directory` is `NULL`
5. `child_setup` is `NULL`
6. The program is of a recognised binary format, or has a shebang. Otherwise, GLib will have to execute the program through the shell, which is not done using the optimized codepath.

If you are writing a GTK application, and the program you are spawning is a graphical application too, then to ensure that the spawned program opens its windows on the right screen, you may want to use `GdkAppLaunchContext`, `GAppLaunchContext`, or set the `DISPLAY` environment variable.

Available since: 2.68

#### Parameters

`working_directory`

  Type: `const gchar*`

  Child’s current working directory, or `NULL` to inherit parent’s, in the GLib file name encoding.

  The argument can be `NULL`.
  The data is owned by the caller of the function.
  The value is a platform-native string, using the preferred OS encoding on Unix and UTF-8 on Windows.

`argv`

  Type: An array of `filename`

  Child’s argument vector, in the GLib file name encoding; it must be non-empty and `NULL`-terminated.

  The array must be `NULL`-terminated.
  The data is owned by the caller of the function.
  Each element is a platform-native string, using the preferred OS encoding on Unix and UTF-8 on Windows.

`envp`

  Type: An array of `filename`

      child's environment, or `NULL` to inherit parent's, in the GLib file
      name encoding.

  The argument can be `NULL`.
  The array must be `NULL`-terminated.
  The data is owned by the caller of the function.
  Each element is a platform-native string, using the preferred OS encoding on Unix and UTF-8 on Windows.

`flags`

  Type: `GSpawnFlags`

  Flags from `GSpawnFlags`.

`child_setup`

  Type: `GSpawnChildSetupFunc`

  Function to run in the child just before `exec()`.

  The argument can be `NULL`.

`user_data`

  Type: `gpointer`

  User data for `child_setup`.

  The argument can be `NULL`.
  The data is owned by the caller of the function.

`stdin_fd`

  Type: `gint`

  File descriptor to use for child’s stdin, or `-1`.

`stdout_fd`

  Type: `gint`

  File descriptor to use for child’s stdout, or `-1`.

`stderr_fd`

  Type: `gint`

  File descriptor to use for child’s stderr, or `-1`.

`source_fds`

  Type: An array of `gint`

  Array of FDs from the parent process to make available in the child process.

  The argument can be `NULL`.
  The length of the array is specified in the `n_fds` argument.
  The data is owned by the caller of the function.

`target_fds`

  Type: An array of `gint`

  Array of FDs to remap `source_fds` to in the child process.

  The argument can be `NULL`.
  The length of the array is specified in the `n_fds` argument.
  The data is owned by the caller of the function.

`n_fds`

  Type: `gsize`

  Number of FDs in `source_fds` and `target_fds`.

`child_pid_out`

  Type: `GPid`

  Return location for child process ID, or `NULL`.

  The argument will be set by the function.
  The argument can be `NULL`.
  The caller of the function takes ownership of the returned data, and is responsible for freeing it.

`stdin_pipe_out`

  Type: `gint*`

  Return location for file descriptor to write to child’s stdin, or `NULL`.

  The argument will be set by the function.
  The argument can be `NULL`.

`stdout_pipe_out`

  Type: `gint*`

  Return location for file descriptor to read child’s stdout, or `NULL`.

  The argument will be set by the function.
  The argument can be `NULL`.

`stderr_pipe_out`

  Type: `gint*`

  Return location for file descriptor to read child’s stderr, or `NULL`.

  The argument will be set by the function.
  The argument can be `NULL`.

`error`

  Type: `GError **`

  The return location for a recoverable error.

  The argument can be `NULL`.
  If the return location is not `NULL`, then you must initialize it to a `NULL` `GError*`.
  The argument will be left initialized to `NULL` by the function if there are no errors.
  In case of error, the argument will be set to a newly allocated `GError`; the caller will take ownership of the data, and be responsible for freeing it.

#### Return value

Type: `gboolean`

`TRUE` on success, `FALSE` if an error was set.